I'm sure it is basic for most, but after browsing the forum for a coupla weeks it finally dawned on me. When the engine is on a few quarts of tranny fluid are sucked into the gears. This is why when draining about 2 qts come out from the fill hole, and while filling it allows you to top off with a bit more fluid.

Eureka

 

Yep, that's why you should research before you try to tackle something. If you can't find what you are looking for, it only takes a couple of seconds to ask...